The present application relates to the field of radiation imaging systems. It finds particular application with the triggering of a data acquisition system of a radiation imaging system that uses charge integrating detector arrays to measure radiation photon flux rates at a detector cell. More particularly, it relates to adjusting an integration period of one or more charge integrating detector cells on the fly during a revolution of the detector array relative to an object under examination.
Today, radiation imaging systems such as computed tomography (CT) systems, single-photon emission computed tomography (SPECT) systems, projection systems, and/or line-scan systems, for example, are useful to provide information, or images, of interior aspects of an object under examination. Generally, the object is exposed to radiation comprising photons (e.g., x-rays, gamma rays, etc.), and an image(s) is formed based upon the radiation absorbed and/or attenuated by interior aspects of the object, or rather an amount of radiation photons that is able to pass through the object. Generally, highly dense aspects of the object absorb and/or attenuate more radiation than less dense aspects, and thus an aspect having a higher density, such as a bone or metal, for example, may be apparent when surrounded by less dense aspects, such as muscle or clothing.
Radiation imaging systems typically comprise a detector array having one or more detector cells. Respective detector cells are configured to indirectly or directly convert radiation photons impingent thereon into electrical charge which is used to generate an electrical signal. The detector cells are typically “charge integrating” or “photon counting” type detector cells (e.g., the radiation imaging system operates in charge integrating mode or photon counting mode).
Charge integrating detector cells, also referred to as energy integrating detector cells, are configured to integrate the electrical charge generated over a period of time (e.g., at times referred to as a integration period or view) to generate a signal that is proportional to an incoming radiation photon flux rate at a detector cell. A tick fence is often used to define the integration period. The tick fence comprises physical markers that are disposed on a stationary gantry. As the rotating gantry rotates, the data acquisition system encounters the physical markers, which triggers the data acquisition system to perform an integration (e.g., readout the charge that has accumulated on respective detector cells and reset the detector cells). An integration period refers to the timespan between integrations of the detector cells. Within a given sector or segment of a revolution of the rotating gantry, there is a static number of integration periods that is defined by the number of physical markers within the sector. Typically, the markers are spaced uniformly over the revolution and thus each integration period represents a defined arc length of the rotation.